Firstly, good luck and practice hard!
As for reason why you stopped the other course, simply state you had some health issues at the time that meant you could not continue at that moment. They usually aren't interested in anything further than that.
I agree entirely with everything that dcstudio mentioned too.
Musicality and technicality are biggies, but this doesn't mean that they are looking for you to play the most difficult piece in the world. If you can demonstrate your abilities BETTER in an easier piece that you're confident with, then go with that.
Also, choose a range of pieces that exhibit different techniques...they need to know you aren't a one show trick.
Oh, if you have a great handspan and can play Liszt, that's always impressive.
Consider Ravel, Gershwin, Bach, Mozart, Chopin, Debussy and Rachmaninov.
Practice as much as you can in front of people, (nursing homes often have pianos and welcome volunteers!), and video yourself playing to listen and watch back.
Good luck, I'm sure you will do super.